Wristwatch with sacrificial pin

ABSTRACT

Device for fastening a bracelet strand to a case of a watch. 
     The device includes at least one fastening element allowing this bracelet strand to be detached from this case when this fastening element is subjected to a predetermined force or moment. 
     Wristwatch including a case and at least one bracelet strand pivotally hinged about a shoulder of a pin forming such a device. 
     This pin is a sacrificial pin which includes, on this shoulder, at least one area of mechanical resistance lower than the lowest mechanical resistance of this case and than the lowest mechanical resistance of this bracelet strand.

This application claims priority from European Patent Application No. 13174090.4 filed Jun. 27, 2013, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention concerns a device for attaching a bracelet or wristlet strand to a watch case.

The invention further concerns a wristwatch including a case and at least one bracelet strand secured to each other.

The invention concerns the field of horology and jewellery, and more precisely the field of assembled units, such as wristwatches, including several components assembled to each other by a hinged connection.

BACKGROUND OF THE INVENTION

The area of assembly of the bracelet or wristlet of a watch or piece of jewellery to a case or to a solid component is always an area where the stresses applied by the user to the bracelet, as a result of his movements, are concentrated. The concentration of forces or of fatigue may cause a deterioration or even breakage of certain components, particularly the horns of the case, or even the watch case itself, particularly when it is made of a plastic material or fragile material. The cost of repair or replacement is high, and damaging for the manufacturer's image.

EP Patent Application No 0246449A1, in the name of ETA, discloses a bracelet whose ends are retained in slots in a watch case by pins partially engaged in grooves each arranged in a face of the slots. There is no detachment of the bracelet from the case when the fastening is subjected to a predetermined force.

U.S. patent application No. 5,235,567A, in the name of GODWIN, discloses a watch bracelet whose ends are folded over themselves and can be immobilised by transverse tubes that form pins and cooperate with transverse holes in the bracelet strands, these tubes being immobilised by a metal wire forming a spring.

FR Patent Application No 2323350A1 in the name of NORMAND discloses a similar system to the above with a linking member with two studs forming pins to cooperate with the horns, connected by elastic material.

SUMMARY OF THE INVENTION

The invention proposes to overcome the problems of the prior art by making it possible to disassemble a wristwatch unit prior to breakage of the case and/or the bracelet. The invention proposes to insert a low cost sacrificial component, which plays the part of a “fuse” and protects the main components and the most expensive components.

To this end, the invention concerns a device for fastening a bracelet strand to a watch case, characterized in that it includes at least one fastening element allowing said bracelet strand to be detached from said case when said fastening element is subjected to a predetermined force or moment.

According to a feature of the invention, said fastening element includes at least one watchmaker's pin including at least one shoulder extending in an axial direction, said pin is a sacrificial pin and includes, on said shoulder, at least one area of mechanical resistance lower than 45 MPa.

The invention also concerns a wristwatch including a case and at least one bracelet strand secured to each other, characterized in that the connection between said bracelet strand and said case includes a fastening element of this type.

According to a feature of the invention, said case and said bracelet strand are pivotally hinged about a shoulder of a pin which forms said fastening element and which is a sacrificial pin which includes, on said shoulder, at least one area of mechanical resistance lower than the lowest mechanical resistance of said case and than the lowest mechanical resistance of said bracelet strand.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will appear upon reading the following detailed description, with reference to the annexed drawings, in which:

FIG. 1 shows a schematic perspective view of a detail of a wristwatch, with the joint between the watch case and a bracelet strand with a fastening element according to the invention.

FIG. 2 shows a schematic cross-section through the axis of a sacrificial pin according to the invention forming this fastening element in a first variant, and fitted into a series of holes comprised in alternate clevis mounts in the case and the bracelet strand, in a first embodiment wherein the sacrificial pin includes notches forming break-off points.

FIG. 3 shows a similar schematic view to FIG. 2 of a second embodiment wherein the pin includes alternate rigid elements and flexible overmoulded elements.

FIG. 4 shows a similar schematic view to FIG. 2 of a third embodiment wherein the pin includes a flexible body overmoulded onto rigid rings arranged perpendicular to the clevis mounts of the case.

FIG. 5 shows a similar schematic view to FIG. 2 of a fourth embodiment wherein the pin includes a rigid body onto which rings made of a flexible material, such as an elastomer, are overmoulded.

FIG. 6 shows a similar schematic view to FIG. 2 of another embodiment wherein a notch forming a break-off point is situated between a horn of the case and the end of the bracelet strand.

FIG. 7 shows a similar schematic view to FIG. 2 of another embodiment wherein a notch forming a break-off point is situated between a pump housed in a blind hole in a horn of the case on the one hand, and the end of the bracelet strand on the other.

FIG. 8 shows a similar schematic view to FIG. 2 of the same first embodiment wherein the holes of the clevis mount of the case are bushed.

FIG. 9 shows a similar schematic view to FIG. 2 of the same first embodiment wherein the holes of the clevis mount of the bracelet strand are bushed.

FIG. 10 shows a schematic perspective view of a second variant wherein the fastening element includes means of absorbing torsion torque, shown here in a particular embodiment with an end link which is more flexible than the bracelet strand.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention concerns the fields of horology and jewellery and more specifically the field of assembled units, such as wristwatches, including several components assembled to each other by a hinged connection.

The invention is described here with a preferred and non-limiting application relating to the securing, particularly of the hinged type, of bracelet strands to a watch case; it could also concern the securing, particularly of the hinged type, of a bracelet strand to a clasp, or even of two components of a bracelet secured and/or hinged to each other.

The invention concerns a device 100 for fastening a bracelet strand 3 to a case 2 of a watch 4.

According to the invention, this device 100 includes at least one fastening element 101 making it possible to detach the bracelet strand 3 from the case 2, when said fastening element 1 is subjected to a predetermined force or moment, and in particular to a traction force of less than 330N. Preferably, fastening element 101 is arranged to break when it is subjected to a force comprised between 300 N and 330 N.

In a first variant illustrated by FIGS. 1 to 9, this fastening element 101 includes at least one watchmakers pin 1, which includes at least one shoulder 10 extending in an axial direction D1. This pin 1 is a sacrificial pin and includes, on shoulder 10 thereof, at least one area 11 of mechanical resistance lower than 45 MPa, in the case of a watch case made of MABS or ABS or similar.

In a second variant, as seen in FIG. 10, fastening element 101 includes at least one end link 103, and this end link 103 is a flexible link including a first end 104 to be secured to case 2 and a second end 105 to be secured to bracelet strand 3, and including means of absorbing torsion torque so that the reduction factor between a torsion torque applied to second end 105 and the resulting torsion torque at the first end 104 is higher than a factor 10. This fastening element 101 may, in particular, be made in a single piece of elastomer material or similar, or a flexible material, so as to absorb most of the torsion moment. It may also include a ball and socket joint with a free connection between the socket and the ball of the joint, or other element.

In an embodiment combining these two variants, end link 103 includes, at the first end 104 thereof, a pin 1 of this type.

The invention also concerns a wristwatch 4 including a case 2 and at least one bracelet link 3 secured to each other. According to the invention, the connection between bracelet strand 3 and case 2 includes a fastening device 100 of this type.

In an advantageous embodiment of wristwatch 4, illustrated in FIGS. 1 to 9, case 2 and bracelet strand 3 are pivotally hinged about a shoulder 10 of a pin 1 which forms both the hinge pin and the fastening device 100 and which is a sacrificial pin. According to the invention, this sacrificial pin 1 includes, on shoulder 10, at least one area 11 of mechanical resistance lower than the lowest mechanical resistance of case 2 and than the lowest mechanical resistance of bracelet strand 3.

Pin 1 secures bracelet strand 3 to case 2, and protects case 2 in the event of extremestressor inappropriate manipulation of the bracelet.

In a particular embodiment illustrated in the Figures, pin 1 includes a plurality of areas 11 of low resistance.

It is understood that, due to the significant stresses imparted by the user to the bracelet, significant stresses are applied to the hinge, and that the invention makes it possible to preselect the sacrificial element, which, in this case, is the least expensive and the easiest to change. Breakage of pin 1 occurs in the event of stresses that are too high, particularly shearing force.

The user visually observes the breakage of pin 1 according to the invention; however the breakage does not necessarily cause the immediate detachment of case 2 and bracelet strand 3, when pin 1 is held at several points.

The configuration of a fragile pin according to the invention is applicable to various types of assembly. FIGS. 1 to 5 show a watch variant including a row of first clevis mounts 5 staggered with a row of second clevis mounts 6 comprised in bracelet strand 3.

FIG. 6 shows another variant where the pin is simply inserted between two end holes 25 of case 2 in horns 24 and it carries a loop 34 of bracelet strand 3. In comparison to FIG. 1, this variant describes the simplest case where there are no staggered clevis mounts but simply a strand with an eye, and a pin between two horns.

FIG. 7 shows yet another variant wherein pin 1 includes pumps 19 at both ends thereof, elastically housed inside blind holes 29 in horns 28 of case 2.

In FIGS. 1 to 5, case 2 includes at least a first clevis mount 5 with a first hole 50 along a first axis D1, and the at least one bracelet strand 3 includes at least a second clevis mount 6 with a second hole 60 along a second axis D2. This bracelet strand 3 is fastened to the at least one first clevis mount 5 of case 2 by sacrificial pin 1. The at least one shoulder 10 is dimensioned to pass into first hole 50 and into second hole 60, to pivotally guide and assemble bracelet strand 3 and case 2. Although, in a simple and economical embodiment, shoulder 10 is cylindrical, and all of first holes 50 are aligned and have the same diameter, as is also the case of all the second holes 60, it is possible to envisage variants having a different geometry. Thus, deformable variants will be seen below wherein shoulder 10 is not cylindrical over the entire length thereof when pin 1 is in the free state. The resistance of pin 1 to traction, shearing, torsion and fatigue, is lower in each case than the respective lowest resistance of case 2 and of bracelet strand 3 which the pin pivotally guides.

In a particular variant with straight clevis mounts, as seen in FIGS. 1 to 5, each first clevis mount 5 includes at least a first lateral face 51 which is radial relative to first axis D1, namely a first lateral face 51 for each end clevis mount 5, and two first lateral faces 51 on both sides of each first inner clevis mount 5. In the same manner, each second clevis mount 6 includes at least one second lateral face 61 which is radial relative to second axis D2, two in the case of the Figures which show more first clevis mounts 5 than second clevis mounts 6. In the position where bracelet strand 3 is assembled and hinged on case 2 by pin 1, the said first clevis mounts 5 are alternated with the second clevis mounts 6 defining interface areas 40 in each of which a first lateral face 51 faces a second lateral face 61, with an axial play JA comprised between 0.000 and 0.060 mm.

This value is suitable for a particular embodiment with a pin 1 made of DIN 1.4404 steel with a diameter of 1.0 mm, a case 2 made of rigid plastic material, such as MABS “Terlux” or ABS “Magnum” or similar, a bracelet 3 that is hinged or made of flexible material, such as flexible plastic material, rubber, leather, steel etc., with holes 50 with a nominal diameter of 1.0 to 1.1 mm, holes 60 with a nominal diameter of 1.0 to 1.2 mm, said holes 50 and 60 could be the holes of DIN 1.4404 steel tubes driven into first clevis mounts 5 and/or second clevis mounts 6.

It is quite clear that the bar according to the invention must be adapted to the case and to the bracelet that it connects, so as to break in the event of excessive load. The employment of the weakest bar can be generalised for all applications.

In any event, pin 1 must break for a force applied in any direction, well below 300 N. In a preferred embodiment, at least one area 11 of low resistance of pin 1 is situated, when bracelet strand 3 is assembled and hinged in position on case 2 by pin 1, perpendicular to an interface area 40, where the shearing stress is highest.

In a variant according to FIG. 8, at least a first clevis mount 5 is bushed with a metal insert 52 including its first hole 50.

However, preferably, the rings are on the bracelet strand rather than on the case, as in FIG. 9.

In a variant according to FIG. 9, at least a second clevis mount 6 is bushed with a metal insert 62 including its second hole 60. This arrangement is advantageous when bracelet strand 3 is flexible, since it allows for rigid guiding of pin 1 and may attenuate wear.

In yet another variant, first clevis mounts 5 are bushed with inserts 51 and second clevis mounts 6 are also bushed with inserts 62.

Advantageously, the peripheral shoulder 10 of pin 1 includes, over the length thereof, first areas 13 of higher resistance alternating with second areas 14 of lower resistance.

FIG. 3 illustrates an example embodiment where first areas 13 of higher resistance are made of rigid metal material or hard plastic material, and where second areas 14 of lower resistance are made of flexible elastomer overmoulded on first areas 13 of higher resistance.

Advantageously, at least one said area 11 of low resistance is formed by the interface area between a second area 14 of lower resistance and a first area 13.

FIG. 3 shows a variant where each first area 13 of higher resistance faces a second hole 60: sections 13 are located perpendicular to second holes 60 of second clevis mounts 6, whereas second areas 14, particularly made of elastomer overmoulded on sections 13 and alternating therewith, face first holes 50 of first clevis mounts 5: said second areas 14 include flanges 141 and 142, pin 1 is inserted into holes 50 and 60 with tightening achieved via these flanges.

FIG. 4 shows tubular sections 13 perpendicular to second holes 60 of second clevis mounts 6, whereas second areas 14, notably made of plastic material such as polyamide or similar, overmoulded onto sections 13 and forming a single piece element over the entire length of pin 1, face first holes 50 of first clevis mounts 5.

FIG. 5 shows the reverse configuration of FIG. 4: it is the core which is rigid and the tubes are made of plastic overmoulded on the pin.

In another variant, which is not illustrated, each first area 13 of higher resistance faces a first hole 50. Tubular sections 13 are perpendicular to first holes 50 of first clevis mounts 5, while second areas 14 made of elastomer overmoulded onto sections 13 and forming a single piece element over the entire length of pin 1, face second holes 60 of second clevis mounts 6.

In some variants, at least one area 11 of low resistance is formed by a second area 14 of lower resistance.

FIGS. 1 and 6 to 9 illustrate variants where at least one area 11 of low resistance includes at least one notch 12 or where every area of low resistance 11 includes a notch 12. This notch preferably has a V-shaped profile or similar, so as to form a break-off point.

In a particular embodiment, pin 1 is made of a plastic material chosen from among polyoxymethylene (POM), polytetrafluorethylene (PTFE) filled with glass fibre to improve its mechanical features, poly(p-phenylsulfide) (PPS) filled with glass fibre to improve its mechanical features, polyamide-imide (PAI), polyether ether ketone (PEEK), or even polybenzimidazole (PBI), or suchlike.

The invention also concerns a sacrificial watchmakers pin 1 including at least one shoulder 10 extending in an axial direction D1 and which includes, on said shoulder 10, at least one area 11 of mechanical resistance lower than 45 MPa, the value depending on the construction and material of watch case 2, said value of 45 MPa corresponds to a case 2 made of MABS or ABS.

This sacrificial pin 1 may be made in accordance with any of the arrangements described above for pin 1 of wristwatch 4 and illustrated in the Figures.

The invention is particularly well suited to the protection of watch cases made of light or fragile materials, such as plastic materials, light alloys, glass, in particular when they are hollow and/or made with walls of small thickness on bracelet fastening elements. The invention offers the advantage of protecting both the case and the associated bracelet strand.

The invention makes it possible to improve a watch simply by replacing, in the initial assembly or after sales-service, existing pins or bars with a sacrificial pin according to the invention, which is inexpensive and requires no modification of the assembly process. 

What is claimed is:
 1. A device for fastening a bracelet strand to a case of a watch, wherein the device includes at least one fastening element allowing said bracelet strand to be detached from said case when said fastening element is subjected to a predetermined force or moment.
 2. The device according to claim 1, wherein said fastening element includes at least one watchmaker's pin including at least one shoulder extending in an axial direction, in that said pin is a sacrificial pin and includes, on said shoulder, at least one area of mechanical resistance lower than 45 MPa.
 3. The device according to claim 1, wherein said fastening element includes at least one end link, and in that said end link is a flexible link including a first end to be secured to said case and a second end to be secured to said bracelet strand, and including means of absorbing torsion torque so that the reduction factor between a torsion torque applied to said second end and the resulting torsion torque at said first end is higher than a factor
 10. 4. The device according to claim 2, wherein said fastening element includes at least one end link, and in that said end link is a flexible link including a first end to be secured to said case and a second end to be secured to said bracelet strand, and including means of absorbing torsion torque so that the reduction factor between a torsion torque applied to said second end and the resulting torsion torque at said first end is higher than a factor 10, and wherein said end link includes, at said first end thereof, a said pin.
 5. A wristwatch including a case and at least one bracelet strand secured to each other, wherein the connection between said bracelet strand and said case includes a fastening element according to claim
 1. 6. The wristwatch according to claim 5, wherein said case and said bracelet strand are pivotally hinged about a shoulder of a pin which forms said fastening device and which is a sacrificial pin which includes, on said shoulder, at least one area of mechanical resistance lower than the lowest mechanical resistance of said case and than the lowest mechanical resistance of said bracelet strand.
 7. The wristwatch according to claim 6, wherein said case includes at least a first clevis mount with a first hole along a first axis, and in that said at least one bracelet strand includes at least a second clevis mount with a second hole along a second axis and is fastened to said at least one first clevis mount of said case by said sacrificial pin wherein said at least one shoulder is dimensioned to pass into said first hole and into said second hole to pivotally guide and secure said bracelet strand and said case, and in that the resistance of said pin to traction, shearing, torsion, and fatigue is lower than the lowest respective resistance of said case and of said at least one bracelet strand.
 8. The wristwatch according to claim 7, wherein each said first clevis mount includes at least a first lateral face which is radial relative to said first axis, in that each said second clevis mount includes at least a second lateral face which is radial relative to said second axis, and in that, when said at least one bracelet strand is in the assembled position hinged on said case via said pin, said first clevis mounts are alternated with said second clevis mounts defining interface areas in each of which a said first lateral face faces a said second lateral face, with an axial play comprised between 0.000 and 0.060 mm.
 9. The wristwatch according to claim 8, wherein at least one said area of low resistance of said pin is situated, when said at least one bracelet strand is in the assembled position hinged on said case via said pin, perpendicular to a said interface area.
 10. The wristwatch according to claim 7, wherein at least one said first clevis mount is bushed with a metal insert including said first hole thereof.
 11. The wristwatch according to claim 7, wherein at least one said second clevis mount is bushed with a metal insert including said first hole thereof.
 12. The wristwatch according to claim 6, wherein said peripheral shoulder of said pin includes, over the length thereof, first areas of higher resistance alternating with second areas of lower resistance.
 13. The wristwatch according to claim 12, wherein said first areas of higher resistance are made of rigid metal material or hard plastic material, and in that said second areas of lower resistance are made of flexible plastic material or elastomer overmoulded on first areas of higher resistance.
 14. The wristwatch according to claim 12, wherein at least one area of low resistance is formed by a said second area of lower resistance.
 15. The wristwatch according to claim 12, wherein at least one area of low resistance is formed by the interface area between a said second area of lower resistance and a said first area.
 16. The wristwatch according to claim 7, wherein said peripheral shoulder of said pin includes, over the length thereof, first areas of higher resistance alternating with second areas of lower resistance, and wherein each said first area of higher resistance faces a said first hole.
 17. The wristwatch according to claim 7, wherein said peripheral shoulder of said pin includes, over the length thereof, first areas of higher resistance alternating with second areas of lower resistance, and wherein each said first area of higher resistance faces a said second hole.
 18. The wristwatch according to claim 6, wherein said pin includes at least one notch in a said area of low resistance.
 19. The wristwatch according to claim 6, wherein said pin is made of a plastic material chosen from among polyoxymethylene (POM), polytetrafluorethylene (PTFE) filled with glass fibre, poly(p-phenylsulfide) (PPS) filled with glass fibre, polyamide-imide (PAI), polyether ether ketone (PEEK), or even polybenzimidazole (PBI). 